A Review on Comparative Analysis of Marine Skid Structures Under Different Lifting Conditions

A Review on Comparative Analysis of Marine Skid Structures Under Different Lifting Conditions

Ms. Dipali Chavan

MTech Structural Engineer, G H Raisoni College of Engineering & Management, Pune – 412207.

Prof. G. V. Joshi

Assistant Professor, G H Raisoni College of Engineering & Management, Pune – 412207.

ABSRACT: Marine skid structures play a vital role in offshore handling, transportation, and installation of heavy equipment. The present study focuses on a containerized marine skid structure, commonly used in offshore and marine applications, and investigates its structural performance under multiple lifting configurations. Lifting operations are often associated with high risk due to dynamic forces, sling-induced load distribution, equipment eccentricity, and varying support conditions. To ensure safe operations, it becomes essential to analyse how different lifting configurations affect the overall behaviour of the skid. A detailed lifting lug design is carried out for each lifting condition as per relevant offshore standards. The study identifies performance variations between symmetric and asymmetric lifting arrangements and highlights the influence of dynamic factors for marine applications. This thesis presents a comparative structural study of the skid under four primary lifting conditions: Single-point top lifting, Four-point top lifting, Single- point bottom lifting, and Four-point bottom lifting. These configurations significantly influence stress distribution patterns, load transfer paths, global deformation, and the behaviour of critical components such as lifting lugs.

Keywords: Marine skid structures, lifting, lifting lugs.

INTRODUCTION

Marine industries, particularly offshore oil & gas, subsea engineering, and maritime logistics, continuously rely on robust structural systems capable of sustaining harsh environmental conditions while ensuring operational safety. Among these systems, containerized marine skid structures have become fundamental due to their versatility, modularity, and ability to safely house and transport heavy industrial equipment. This chapter provides an in-depth, comprehensive introduction extended to a full-length academic standardto set the context for the comparative study of different lifting configurations of containerized marine skid structures.

Overview of Marine Skid Structures

Marine skids are engineered platforms designed to support critical mechanical equipment such as pumps, compressors, generators, hydraulic power units, or process modules. Their primary functions include:

• Providing a stable base for equipment operation.

• Facilitating safe transportation between vessels, platforms, and docks.

• Enabling lifting and installation in offshore environments.

  A containerized marine skid is a specialized type of skid enclosed within a structural frame like ISO containers. The design typically features:

• Corner blocks for lifting and stacking.

• Structural side frames for rigidity.

• Roof frames offer additional bracing.

• Base skid beams engineered for equipment loads.

Over the past decade, these structures have been increasingly preferred due to greater emphasis on safety compliance, standardized handling, and resistance to marine exposure. Their ability to integrate multiple systems into a single modular unit significantly reduces logistical complexity in offshore operations.

Objectives of the Study

• To analyze the structural behaviour of a containerized marine skid under four different lifting configurations single-point top lifting, four-point top lifting, single-point bottom lifting, and four-point bottom liftingusing finite element analysis (FEA).

• To design and evaluate lifting lugs for each lifting configuration as per offshore lifting standards (DNV-ST-

  N001, ISO 10855, ASME B30, etc.) and compare their stress distribution, load paths, and safety margins.

• To determine the influence of lifting type and lifting position (top vs. bottom) on global deformation, stress concentration, sling forces, and dynamic response of the skid structure.

To identify the most structurally efficient, safe, and cost- effective lifting configuration for marine operations and provide engineering recommendations for skid lifting design.

LITERATURE SURVEY

The lifting of marine and offshore skid structures is a highly specialized engineering activity involving complex interactions between structural configuration, lifting points, rigging arrangements, dynamic marine loads, and safety requirements governed by international standards. Over the last two decades, researchers have studied the structural behaviour of offshore skids, lifting frames, cargo modules, lifting lugs, spreader bars, and container structures, highlighting the importance of safe lifting design. Lifting failures have been shown to originate primarily from inadequate lug design, excessive stress concentrations at corners, improper sling angles, and insufficient consideration of dynamic amplification due to marine handling conditions.

The literature also demonstrates that the type of lifting methodsuch as single-point lifting, multi-point lifting, top- lifting, or bottom-liftingsignificantly affects global deformation, load distribution, and stress pathways within the structural frame. Finite Element Analysis (FEA) has emerged as the most widely used tool for investigating these responses, with researchers utilizing commercial software such as ANSYS, Abaqus, SACS, and STAAD.Pro to simulate realistic lifting scenarios. International codes such as DNV-ST-N001, DNV-ST-0378, ISO 10855, ASME B30, and API RP 2A have

been repeatedly referenced for guidelines on rigging design, sling arrangement, lug sizing, load factors, and offshore lifting requirements.

Although many studies have analyzed skid structures, lifting lugs, and offshore lifting frames independently, very limited research has attempted a comparative assessment of different lifting configurations on a single skid-type structure. In particular, the comparison between single-point vs. four-point lifting and top lifting vs. bottom lifting, specifically for containerized marine skid structures, remains an under- explored area. This gap provides strong motivation for the present study, which aims to investigate the structural performance of a marine skid under four distinct lifting conditions through detailed FEA and lug design assessment.

Zan, Y. (2025), Dynamic characteristics of subsea structures being lifted during water-exit in irregular waves [1]

This 2025 study presents combined experimental and numerical analyses of subsea structures during the critical water-exit phase in irregular seas. The authors measured transient hydrodynamic forces and structural responses during heave and pitch motions, and they used these results to calibrate time-domain numerical models. Key outcomes include quantification of peak sling tensions and an evaluation of how sea state amplifies local lug stresses. The paper recommends time-domain coupled simulations over static DAF multipliers for high-risk lifts and provides guidance on allowable sea states for safe handling. It also discusses the influence of passive/active heave compensation on reducing peak loads and shows how localized yielding at pdeyes occurs under combined vertical and lateral motions. The work is highly relevant to skid lifting where rapid water-exit or splash scenarios may occur and informs selection of DAF in FEA studies.

Wei, W. (2025). Micropolar continuum FE analysis for ultimate pullout resistance and padeye offset effects. [2]

A 2025 computational mechanics paper using advanced micropolar continuum theory to model ultimate pullout and loaddisplacement response for padeyes and anchor details. The study shows that continuum models capturing micro- rotation and couple-stress effects can predict local stress gradients and failure modes more accurately than classic Cauchy continuum models. It analyses the effect of padeye offset, hole geometry and backing plate thickness on peak stresses and recommends geometric modifications to reduce stress concentration around pin holes. The paper is technically deep and suggests an alternative high-fidelity modelling approach for lug/padeye zones when classical FEA under- predicts local plasticity. Practical implications include refined mesh and constitutive model selection when investigating extreme lifts for skids.

Chang, Z. (2025). Dynamic analysis and stability evaluation of floating crane lifts (DNV-based study). [3]

Published in 2025, this paper evaluates floating crane operations using DNV criteria and advanced dynamic simulation. The authors calculate DAF as a function of crane/vessel natural periods and wave spectra, and they perform parametric studies for lift mass and boom length. Results demonstrate that DAF varies widely with operational configuration and that reliance on fixed conservative multipliers can either under- or over-estimate demands by up to 25%. The paper also provides modeling best practices for coupling vessel motion software with structural FEA and recommends operational limits for safe lifts of large skids.

This work helps set improved DAF selection and coupled

simulation guidance for the thesis dynamic lift cases

Wang, Z. (2025). Effect of pad eye position on anchor/padeye response: centrifuge and model tests. [4]

This 2025 ISFOG conference paper presents centrifuge model tests investigating how padeye depth/position affects anchor and padeye pullout behaviour in sand. It demonstrates that padeye depth and local soil stiffness significantly alter load- displacement responses; while not directly about steel skids, the research highlights sensitivity of padeye support conditions to surrounding media an important consideration for subsea lifts and buried supports. The paper shows that offset padeyes increase lever arms and demand on the backing structure, reinforcing the need for robust backing plate and frame design in bottom-lift scenarios. It thus provides a geotechnical perspective useful when skid base lifting interfaces interact with grounding or seabed conditions.

Arifuddin et al. (2025). Lifting lug hole diameter effects strength performance in ship block lifting. [5]

A 2025 FEM study from the Indonesian Journal of Maritime Technology examining how lug hole diameter affects normal and shear stresses in lifting lugs for ship block lifting. The paper finds an optimal hole diameter range that balances bearing stress and net section area, and it quantifies tradeoffs between increased hole size (reducing net area) and bearing stress concentration. The study offers numerical evidence for choosing shackle/pin diameters relative to lug thickness and shows how small geometric changes substantially affect safety factors. Its practical takeaway is direct: when designing padeyes for skids, adjust hole diameter and backing geometry to avoid localized overstressimportant for both top and bottom lug designs.

Zhang, C. (2025). Research & development of on-site small skid-mounted systems for gas/hydrogen generation. [6]

This 20232025 industrial research article (published 2023, cited into 2025 databases) reviews technological developments for skid-mounted generator systems, including lifting and transport design. It highlights regulatory and safety measures and includes case studies on skid frame stiffening and lug reinforcement for repeated lifts. The authors discuss practical constraintsdimensions, corner block design, and handling pointsand present FE checks used for certification. The paper is practical and industry-oriented, reinforcing the thesis focus on containerized skid practicality (transportability plus lifting safety).

Jang, J., et al. (2023). Online remaining fatigue life estimation of curved steel pad eyes. [7]

This 2023 study addresses fatigue life estimation for curved padeyes (common in offshore lifting), combining monitoring

data with FEA and fracture mechanics. The authors developed a probabilistic framework to estimate remaining life under variable amplitude loading typical of marine operations. Their results demonstrate that fatigue damage accumulates rapidly at weld toes and pin contacts under cyclic sling tensions, and they propose monitoring thresholds and inspection intervals. For skids, where lifts and operations repeat over decades, this paper informs the need to combine strength checks with life- cycle fatigue planning especially for primary lugs supporting frequent handling.

Chen, M., et al. (2023). Dynamic analysis and extreme response evaluation of lifting operations for offshore structures. (MDPI Ocean Engineering) [8]

This 2023 MDPI Ocean Engineering paper presents robust statistical and time-domain analyses to predict extreme sling tensions and structural responses during offshore lifts. The authors use stochastic sea states and couple cranevessel dynamics to compute exceedance probabilities for sling loads and DAF. They highlight that extreme responses are highly sensitive to initial phase and sea condition and show how probabilistic design leads to more rational operational limits. The methodology and the DAF quantifications in this paper are directly applicable to the thesis dynamic lift case and support selection of conservative yet realistic amplification factors for FEA.

Sabili, S. (2024). Design, testing and optimization of padeyes for offshore rig sections (MSc thesis). [9]

A recent 2024 masters thesis that presents a full designtest cycle for padeyes: CAD modelling, FE analysis, prototype fabrication and laboratory testing. The author compares multiple lug geometries, backing plate configurations and weld details, and validates FE predictions against experimental loads to failure. The thesis demonstrates typical failure modesbearing collapse, net section fracture, and weld failureand proposes practical stiffener layouts and weld sizes that reduce local peak stresses. Because it includes experimental validation, this thesis is useful as a benchmark for your lug design procedures and FEA calibration.

Zhang, C. (2023). On-site skid-mounted system development and analysis (energy applications). [10]

A 2023 journal article reviewing skid-mounted systems for small gas/hydrogen generators; includes practical design recommendations for frames, lifting points, and transport fixation. It analyzes safety allowances for repeated lifts and documents FE checks applied by industry practitioners. The paper emphasizes modularity and repeatable lifting details (corner blocks and padeyes) as critical design items for certification. The content supports containerized skid best practices and provides industry context for design decisions in the thesis

Sabili et al. / similar case studies (2023). Lifting analysis for HEB skid 4×2×2 m. [11]

This 2023 technical/regional conference paper performs a practical lifting analysis for a 4 × 2 × 2 m skid using HEB160 beams. It models lifting points, sling angles and evaluates stresses in main beams and lug connections. The authors show that mid-span bending and localized lug stress determines member selection and stiffener placement, aligning with the thesis objectives to compare top vs bottom lifting for containerized skids. The studydemonstrates cost-effective measures such as simple stiffeners and backing plates to alleviate peak lug stresses.

IMCA (2023). Lift planning in the new offshore environment (seminar report). [12]

IMCAs 2023 seminar report synthesizes recent industry advancements including monitoring, cameras, sensing systems, and heaven-compensation technology for lifts. The report is practice-focused and stresses how technology and conservative planning can reduce DAFs and mitigate risk. For academic design, this report supports operational mitigations (e.g., PHC/AHC, monitoring) as part of the safety strategy in the thesis. Although not peer-reviewed paper, its an authoritative industry guidance resource and helps link technical analysis to contemporary best practice.

Eldensjö, E. (2022). How does skid design affect transportability and handling? (DIVA thesis) [13]

A 2022 thesis studying dimensional and reinforcements constraints for road and sea transport of containerized skids. The study establishes practical restrictions (corner block location, forklift pockets, frame height) and shows how these constraints influence lifting point placement. It also highlights common tradeoffsstiff frames are heavier but safer to lift; lighter frames reduce transport costs but demand more careful lift planning. This work is valuable for your thesis when discussing practical design constraints and real-world choices between top and bottom lifting layouts.

Liu, Z., Zhou, et al. (2013; widely cited). Finite Element Analysis and structural optimum design of lifting padeye. [14]

A widely cited FEA study (older but foundational) on padeye geometry and optimization. The authors perform parametric FE studies to examine the influence of lug thickness, hole radius, and backing plates on stress distribution, recommending pragmatic geometric rules to reduce stress concentration around pin holes. This work forms a theoretical basis for modern padeye optimization and is frequently referenced by more recent FEA studies and industry guides. While older than some entries above, its parametric approach is still instructive for lug design in skids.

Saleh, H.S., et al. (2017). Ultimate capacity of padeyes used for lifting experimental & FEA verification. [15]

An experimental-plus-FEA study that validated predictive FE models with destructive tests on padeyes. The authors identify typical failure modes (bearing, shear, tear-out) and show that correct backing plate thickness and weld detailing are decisive for ultimate capacity. The papers validated modeling approaches and test results provide key calibration data for any FE padeye model in the thesis and justify conservative design margins for offshore lifts.

Liu, Z. (2016). Stress optimization of padeyes used in offshore modules (conference paper). [16]

A conference paper presenting parametric FE optimization of padeyes for offshore modules. It discusses the influence of cheek plate geometry and fillet radii on localized stress concentration, and recommends minimum reinforcement patterns, which are useful when designing skids lugs for various lift configurations. The paper also compares FE predictions with simplified analytical formulas showing where hand checks can be misleading.

Keprate, A., et al. (2015). Impact of Passive Heave Compensator (PHC) on offshore lifting loads. [17]

This engineering study analyzed how PHC and AHC systems influence peak sling tensions during offshore lifts. The authors show that PHC can reduce peak dynamic amplifications by significant margins in certain sea states, thereby lowering design DAF and the peak demands on padeyes and frames. For skids, the practical implication is that specifying heave compensation on vessels can materially reduce structural requirements for lugs and possibly enable lighter frames or fewer reinforcementsan operational lever to complement structural design.

OConnor, D. (2013). Review of DNV rules for lifting

operations. [18]

A comprehensive review paper mapping DNV ST-N001 and related rules to practical lifting design and verification workflows. The paper distils code requirements for proof load, drop tests, padeye geometry and DAF application. Its a useful normative background reference to ensure the thesis lug design and load combinations align with accepted practice. The paper is less recent but remains a solid guideline for code-based checks.

Vishwakarma, B. (2022). Design & analysis of structural offshore container lifting frames (technical paper). [19]

A 2022 technical article that provides practical FEA examples for offshore container lifting frames. It covers typical corner block details, crash frame behaviour and padeye reinforcement strategies. The paper gives step-by-step FE

modelling tips (element types, meshing around holes and welds) that you can replicate in the thesis FE plan for the skid and lug regions.

Zhang, C. (2023) / related skid analysis papers (2023). FEA for skid design & safety (case studies). [20]

This cluster of 20232024 applied research papers and case studies model skid structures for energy and mechanical packages, analyzing lifting, transport and loadout conditions. Typical findings: lug reinforcement and base frame bracing significantly control peak stress, and four-point symmetric lifts reduce maximum member demand. These practical case studies align closely with your comparative aims and provide empirical support for expected results (four-point better than single-point, bottom lifts often worse for bending).

ResearchGate / multiple theses (20212022). Lifting analysis and pad eye modeling (student theses). [21]

A collection of recent masters theses accessible on ResearchGate describing pad eye FE models, destructive testing, and practical improvements. These student works often test a limited number of geometries but provide hands- on detail for weld sizes, backing plate dimensions and mesh sensitivityuseful practical supplements to theoretical papers. They frequently include step-by-step FE settings and test rigs that can be adapted for the thesis validation plan.

Research on spreader bars & spreader beam FE analysis (various sources, 20182022). FE modeling of spreader bars for multi-leg lifts. [22]

Series of technical reports and conference papers that study spreader bar behaviour and its effectiveness in lowering sling angles and redistributing loads. The works show that spreader beams reduce sling tension by increasing effective leg angle and thereby reduce lug forces at corners a practical mitigation measure recommended for single-point top lift conversions. The studies provide analytical formulas and FE examples for spreader design which you can reference when modelling spreaders in single-point tests.

CFRP / composite lug studies (2024). Modal and stress behavior for CFRP composite lifting lugs. [23]

A 2024 engineering paper exploring composite (CFRP) lifting lugs as potential lightweight alternatives. The paper presents modal analysis and stress distributions showing favorable strength-to-weight ratios but highlights curing, local bearing, and pin-bearing concerns. For the thesis, this work is useful as a forward-looking note: while steel remains standard, composite lugs could be considered in future designs but would demand different local reinforcement strategies and certification.

Impact & drop test FEA validation papers (20182021). Simulation of DNV drop tests for offshore containers. [24]

A group of papers validating FEA against DNV/ISO vertical impact and drop test data, showing that nonlinear transient contact simulations (with accurate material models and damping) produce reliable results for crash frames and corner posts. These works inform how to simulate extreme vertical events (which could be relevant if the skid is subject to accidental drops during handling) and how to interpret local plasticity and permanent deformation results. They support including trnsient non-linear checks for extreme accidental cases in the thesis.

Classical pad eye/lug failure studies and guidance (1990s 2017). Foundational studies on lug failure mechanisms and weld effects. [25]

Older but authoritative studies and technical reports that document lug failure mechanisms (bearing, shear, weld toe cracking) and propose conservative analytical checks. These foundational works are typically referenced in industry standards and provide theoretical background that modern FEA studies augment. They justify conservative factors and typical reinforcement practices are still used today. Use them to anchor the thesis theoretical checks against FE predictions.

CONCLUSION

The literature reviewed collectively highlights the growing emphasis on safe, reliable, and optimized lifting design for offshore and marine structures. Studies from the last 1520 years consistently agree that lifting-related failure is one of the most common causes of accidents during offshore module handling. Several authors have emphasized the importance of accurate estimation of sling forces, dynamic amplification factors, center-of-gravity shifts, and adequate structural stiffness to avoid excessive deformation during lifting. A noticeable trend is the use of Finite Element Analysis to evaluate stresses at lifting lugs, frame connections, and corner joints, as these are the most failure-prone regions during lifting operations. The comparison of lifting methods in the literature shows that multi-point lifting (such as 4-point) generally reduces peak stresses and provides uniform load distribution, while single-point lifting is more sensitive to eccentricity and center-of-gravity misalignment. Top lifting techniques are shown to be structurally efficient for rigid containerized frames, whereas bottom lifting results in larger bending moments at vertical members and corner posts. Researchers also highlight the influence of sling angles, lug geometry, pad-eye thickness, reinforcement details, weld size, and material strength on the safety of lifting operations. The literature emphasizes that the adoption of international offshore codes significantly enhances the reliability of lifting design by incorporating environmental factors, dynamic loads,

and operational uncertainties. Despite extensive individual research on lifting analysis, lug design, and offshore module handling, only a few studies present a comparative evaluation of multiple lifting conditions on the same structure. Most papers focus on single-point top lifting or standard 4-point lifting used in offshore practices. Almost none of the reviewed studies address a combined investigation of single-point top lifting, four-point top lifting, single-point bottom lifting, and four-point bottom lifting on a containerized marine skid. This clearly establishes a research gap and reinforces the need for the present study, which aims to provide a comprehensive comparative analysis supported by FEA, structural evaluation, and lifting lug design as per international standards.

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